Minimal Risk for Soybean Rust in Southeast

Source: Farm Press | Jul 07, 2010

Asian soybean rust[4] (ASR) is getting a later than usual start in the lower Southeast and isn’t expected to reach high-acreage soybean[5] production areas of North Carolina and southeast Virginia in time to do any damage. The one caveat, veteran rust watchers warn, is a heavier-than-usual hurricane season that can move the disease-causing fungal spores much more rapidly than their normal north to south movement.

North Carolina Soybean Specialist Jim Dunphy says development of ASR for the 2010 growing season is likely, but warns growers about the fickle nature of weather, especially tropical storms and hurricanes.

Scorching daytime temperatures approaching 100° F and hot, humid nighttime readings common so far in the lower Southeast are not conducive to development of ASR. The potentially damaging fungal disease moves generally south to north throughout the soybean growing season.

On June 28 the first rust of the growing season was reported in the Florida Panhandle, east of Tallahassee – but on kudzu, not soybeans. The kudzu is in an area where rust has been found the past few years and was found back in the winter.

This particular patch of kudzu was under pine trees near a pond, so it may have been somewhat buffered from killing cold temperatures during the winter.

Auburn University plant pathologist and rust watcher Ed Sikora reports, "On June 23, soybean rust was detected on 10 kudzu leaves growing along an abandoned building in Mobile, AL. Rust was not detected in multiple kudzu patches scouted near this positive site. The amount of inoculum appeared to be extremely low based on our observations.

“Soybean rust had been observed over-wintering on kudzu growing inside an abandoned building near this site. However, that kudzu was mechanically destroyed in March. The risk of soybean rust appears to be very low for growers in south Alabama at this time," Sikora says.

The first U.S. citing for rust in 2010 occurred in extreme south Texas, along the Mexico border. In addition to the live spores found in southwest Alabama, disease-causing spores have been found in two counties in Georgia, one in Florida and four in Louisiana.

Plant pathologists in Florida and Georgia concur with Sikora’s projection of low risk to soybeans in their states.

Low risk in the soybean-producing areas of Alabama, Florida and Georgia typically means low risk to growers in the Carolinas and Virginia. The trump card, however, could come in the form of tropical storms and hurricanes, which typically follow an El Niño year.

Dunphy says, “Soybean rust is unlikely to spread appreciably from Mobile, but we now know it is alive and well in the U.S. with the previous finds in Texas and Mexico.

Traditionally, rust has moved from Florida up the East Coast to North Carolina. Considering the length of time it has taken to reach North Carolina from Florida/Georgia in the past, and the hot dry conditions current in much of the U.S., it seems unlikely to impact North Carolina this growing season.

“We – North Carolina State University Plant Pathologist Steve Koenning and myself – reserve the right to alter the prediction should a tropical storm develop that would transport spores,” Dunphy says.

Soybean acreage in North Carolina is expected to be down by 8-10% in 2010. Still, with more than 1.6 million acres planted, tracking soybean rust movement is critical to the state’s agricultural economy.

In Virginia, soybeans remain the top row-crop with nearly a half million acres. In 2010, soybean revenues are expected to push near $150 million.

Nationwide soybean acreage is expected to be up slightly, with the biggest increases expected in Kansas and Iowa and the biggest decreases in North Carolina and Georgia.

The biggest reason for reduced soybean acreage in the upper Southeast is the resurgence of cotton acreage. In North Carolina, the USDA[6] pegged cotton planting at 44% higher than 2009. Similar, though much less dramatic increases are expected in South Carolina and Virginia.

Increases in cotton acreage take many of the contiguous acres of soybeans out of the equation. Increases in cotton acreage in Georgia and Alabama, combined with continued hot, dry weather conditions bode well for a lack of rust problems in soybeans in the upper Southeast.

As with any crop, and any disease of crops, there is no guarantee that problems won’t occur. However, based on nearly 10 years of tracking data and history of movement of the disease, 2010 looks like the least likely of years for rust problems to crop up, especially farther north in the Southeast soybean producing belt.